Sliding vane pumps are disclosed in U.S. Pat. Nos. 4,746,280, 4,830,593 and 5,431,552. In a sliding vane pump, the pump casing can include a stationary liner having an inner surface eccentric with respect to an axis of the rotor held within the casing. A plurality of radial slots are arranged in the rotor and each slot holds a vane that is slidably extendable and retractable within the slot. Inlet and outlet openings are arranged around the periphery of the liner in select regions. The fluid enters the inlet openings and is trapped between the rotor and the liner between adjacent moving vanes which are extended outward from their respective slots as the rotor rotates. The fluid is then moved around the interior of the liner with the rotating rotor until the fluid is passed through the outlet openings.
The vanes, sometimes referred to as "blades", must be strategically biased radially outward either by springs or, in some cases, hydraulic pressure of the fluid being pumped. U.S. Pat. No. 5,431,552, which is owned by the assignee of this application, discloses a liner or cam design which enables the vanes to remain more positively actuated during the pumping operation, thereby increasing the pump efficiency while reducing system noise and vibration. The disclosure of U.S. Pat. No. 5,431,552 is incorporated herein by reference.
One problem associated with currently available vane pump designs is the large amounts of maintenance required during the lifetime of such pumps. Specifically, in order to service the rotor bearings, the pump must be substantially disassembled, including the inlet and outlet piping. Often, the prime mover must be removed and the wiring connecting the pump to a power supply must be disconnected. The removal of the companion piping, the prime mover as well as the substantial disassembly of the pump simply to change the rotor bearings is inefficient and time consuming.
Further, in currently available vane pumps, it is difficult to reverse the flow of such pumps. Again, substantial disassembly of a pump is required which often requires the companion piping, prime mover and electrical connections to be disconnected.
Accordingly, there is a need for an improved vane pump design which is both efficient, like the pump disclosed in U.S. Pat. No. 5,431,552, but also which is easier to maintain in terms of the service of the rotor bearing and which is easier to reverse the flow thereof.